Doherty power amplifiers use efficient and linear power amplifier configurations and are often employed to amplify radio-frequency (RF) signals having varying amplitudes. The Doherty power amplifier (PA) configuration generally includes two amplifier sections, the first section, referred to as the carrier PA, can cater for lower amplitude signals, and second section, referred to as the peaking PA, provides the capability to meet the higher power-level conditions (e.g., at a peak power above ˜6 dB power back-off) without running into compression. In the Doherty PA configuration, the input power signal is split into two components, each of which is sent to one of carrier PA and the peaking PA. The output signal from the carrier PA is 90° phased shifted (e.g., via a quarter-wavelength transmission-line).
The Doherty PA configuration, although can be readily implemented using on-board transmission-line traces and may be a robust configuration, but may not be a viable choice for integration on a chip. This is because the quarter-wavelength transmission-line may have a large area and may result in an unacceptable substrate loss. Further, the Doherty PA configuration may be difficult to migrate to a differential PA topology.